1. Field of the Invention
The present invention relates to a semiconductor processing system and a vaporizer for generating water vapor from purified water. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an FPD (Flat Panel Display), e.g., an LCD (Liquid Crystal Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
As one of the semiconductor manufacturing processes, there is a heat process for processing a semiconductor wafer within a water vapor atmosphere. For example, in the case of forming a silicon dioxide film to fill a recess having a high aspect ratio, a good filling property can be obtained by applying polysilazane coating liquid onto the substrate and then performing a heat process thereon. In this case, the film quality is improved by gradually increasing the process temperature while performing the heat process on the coating film. A representative heat process of this kind is a wet oxidation process for oxidizing the surface of a silicon film. Further, in a dry oxidation process using oxygen gas, there is a case where water vapor is supplied onto a wafer to form a very thin wet oxidation film in the step of increasing the temperature to a process temperature. For example, Jpn. Pat. Appln. KOKAI Publication No. 7-142461 (Patent Document 1) and Jpn. Pat. Appln. KOKAI Publication No. 2004-247124 (Patent Document 2) respectively disclose two typical methods for supplying water vapor.
In the method disclosed in Patent Document 1, liquid purified water is atomized by a nozzle, and liquid droplets thus formed are heated to generate water vapor. According to this method, the structure for generating water vapor is simple, and the amount of water vapor can be easily controlled by adjusting the carrier gas flow rate and/or heater output. However, where such a unit is used for performing a heat process, a large number of particles are observed on the surface of a wafer treated by the heat process. These particles deteriorate the yield of the wafer or diced chips, which becomes prominent with a decrease in the film thickness of semiconductor devices and a decrease in the size of patterns. The mechanism of this particle generation has not yet been clarified.
In the method disclosed in Patent Document 2, oxygen gas and hydrogen gas are caused to react with each other by catalysis to generate water vapor. Since a gas having a high purity can be more easily obtained than a liquid, this method may be preferential in decreasing impurities, such as metal, to be mixed, as compared to the method using liquid purified water. However, in order to increase the generation amount of water vapor, the catalysis needs to be increased and thereby brings about a high cost, because the catalysis consists mainly of platinum. Further, according to this water vapor reaction mechanism, if the amount of catalysis is simply increased, the reaction temperature becomes hard to control. For this reason, it is necessary to increase the volume of a generating portion or the number of generating portions in accordance with the generation amount of water vapor, which is disadvantageous in cost. Further, since hydrogen is used, a special countermeasure is required to confirm safety.